Japanese pear tree named `Kotobuki Shinsui`

ABSTRACT

The new and distinct cultivar relates to a russet type Japanese pear tree that has a strong resistance to black spot disease and has substantially the same excellent qualities as the Japanese pear cultivar `Shinsui`. The new pear tree bears a yellowish brown fruit, is highly sweet, medium in acidity, and has a rich taste that is suitable for dessert use.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct cultivar of Japanesepear tree (Pyrus pyrifolia), and particularly to a russet type pear treehaving characteristics substantially the same as those of `Shinsui`(unpatented in the U.S.), but having a significantly strong resistanceto black spot disease.

In Japan, `Shinsui`, which was obtained from the crossing of `Kikusui`(seed parent)(unpatented in the U.S.) and `Kimizuka Wase` (pollenparent)(unpatented in the U.S.) and was released in 1965, is a popularcultivar. The fruit of `Shinsui` ripens and can be eaten 7 to 10 daysearlier than that of `Kosui` (unpatented in the U.S.), and the taste ofthe fruit is sweet and rich. It has, however, a shortcoming in that`Shinsui` is susceptible to black spot disease. Black spot diseasedevelops in the leaves, stems and fruits of the `Shinsui` tree. Inparticular, the young fruit is associated with the formation of blackand rounded lesions and cracks. It is necessary to take care that`Shinsui` not be infected with the disease, thus, `Shinsui` is graduallydecreasing in popularity. One object of the present invention is toprovide an improved cultivar of the pear fruit tree having a strongresistance to black spot disease, while also having the excellentcharacteristics of the `Shinsui` cultivar.

ORIGIN AND A SEXUAL REPRODUCTION OF THE CULTIVAR

The new cultivar of Japanese pear tree was derived from `Shinsui` bymutation breeding. Since 1987, many scions of `Shinsui` were exposed toγ-rays and the scions were top-grafted on mature trees. Leaves of grownvegetative shoots were tested using crude toxin of black spot disease,i.e., AK toxin. In 1989, among the scions exposed to γ-rays at a rate of2.5 Gy/hour for a total radiation dose of 80Gy, one of the scions havinga distinctively stronger resistance to black spot disease than theoriginal cultivar `Shinsui` was found. It has been confirmed that thevariant grown from the scion has a significantly stronger resistance toblack spot disease than `Shinsui`. Branches of the new variant weregrafted on rootstocks of the variety `Hakko` and/or top-grafted onmature trees to study their characteristics such as vigor in the field.

As the trees bore fruits for the first time in 1991, the fruitcharacteristics were studied. Since then, is has been determined thatthe trees of the new variety have a significantly stronger resistance toblack spot disease than `Shinsui`, while also displaying the excellentcharacteristics of `Shinsui`. For instance, the trees of `KOTOBUKISHINSUI` had only slight lesions of black spot disease on the shoots andyoung fruit; little or no defoliation or abscission of fruit due toblack spot disease infection was observed in filed tests. Meanwhile,`Shinsui` had developed lesions due to black spot disease infection onthe shoots and young fruit and defoliation or abscission of fruit wasobserved in plants cultivated without bagging.

This new and distinct cultivar of Japanese pear tree was asexuallyreproduced by grafting at the various Prefectural Experimental Stations(Tsukuba-shi, Ibaraki-ken; Kuki-shi, Saitama-ken; Chiba-shi, Chiba-ken;Takamori-machi, Shimoina-gun, Nagano-ken, and Daiei-cho, Tohaku-gun,Tottori-ken), and the homogeneity and stability thereof was confirmed.The new cultivar was named `KOTOBUKI SHINSUI`.

The new cultivar of Japanese pear tree according to the presentinvention was developed from `Shinsui` by mutation breeding using γ-raysas a mutagen. As described above, `Shinsui`, the parent cultivar, wasobtained from the crossing of `Kikusui` and `Kimizuka Wase` and iswidely cultivated in Japan. The main characteristics of `Shinsui` thatdiffer from the instant cultivar are as follows:

Tree:

Vigor.--New shoot growth averaged 183 cm in 1999.

Spurs.--In 1999, and average of 15.1 per meter of a branch.

Branches (shoot):

Length of internode.--Short, about 3.9 cm.

Leaves:

Size.--Medium (12.6 cm long by 7.6 cm wide).

Flowers:

Number of petals.--Slightly more than medium, 5.1 per flower on average.

Number of stamens.--Slightly more than medium, 27.0 on average.

Amount of pollen.--High.

Fruit:

Size.--Small, 319 g on average in 1992.

Size of core.--Ratio of transverse diameter of core to transversediameter of fruit is medium, 24.9/84.2.

Taste.--Sugar content of juice, about 13.8%; medium acidity, pH 4.7; noastringency.

Maturity.--Ripening early in the season, e.g., August 15th-24th at theTottori Prefecture, Japan.

Resistance to Diseases: Has a susceptibility to black spot disease andhas minor susceptibility to pear scab, pear canker and Physalosporacanker. The tree is not susceptible to pear necrotic spot virus. Thecultivar `Shinsui` is widely cultivated, and its nursery stock is easilyavailable in Japan.

SUMMARY OF THE INVENTION

The characteristics of the new cultivar of Japanese pear tree `KOTOBUKISHINSUI` are substantially the same as those of `Shinsui`, with theexception of those enumerated above and the additional exception that`KOTOBUKI SHINSUI` has an obviously stronger resistance to black spotdisease than `Shinsui`. The new cultivar can be cultivated under thesame controls as `Kosui` or `Hosui` (unpatented in the U.S.), which areboth resistant to black spot disease.

The new cultivar has strong vigor. The shoots are dark brown. Althoughthe new cultivar has few axillary flower buds and many spurs, the spurshave a tendency to be blind buds. The flower buds are oval in shape andbrown in color.

Flowering time is a little earlier than that of `Kosui`. The flowershave less petals than those of `Kosui` and the color of the anthers isdeep red, deeper than those of `Kosui`.

The fruit size is small (about 250-300 g). The fruit is oblate and theuniformity of the fruits is good. The color of the fruit skin isyellowish brown. The flesh is yellowish white and is more yellowish thanthe flesh of `Kosui` in color and slightly softer and rougher intexture. The sugar content of the fruit is about 13.6%, slightly higherthan that of `Kosui`.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of the new cultivar, `KOTOBUKI SHINSUI`, astrained.

FIG. 2 is a photograph of the branches of `KOTOBUKI SHINSUI`.

FIG. 3 is a photograph of the adaxial adult leaves of `KOTOBUKISHINSUI`.

FIG. 4 is a photograph of the abaxial adult leaves of `KOTOBUKISHINSUI`.

FIG. 5 is a photograph of the side view of the flowers of `KOTOBUKISHINSUI` in the bud stage.

FIG. 6 is a photograph of the flowers of `KOTOBUKI SHINSUI`.

FIG. 7 is a photograph of the fruit of `KOTOBUKI SHINSUI`.

FIG. 8 is a photographic view of the stem end of the fruit of `KOTOBUKISHINSUI`.

FIG. 9 is a photographic view of the blossom end of the fruit of`KOTOBUKI SHINSUI`.

FIG. 10 is a photograph of a longitudinal sectional view of fruits of`KOTOBUKI SHINSUI`.

FIG. 11 is a photograph of a cross-sectional view of fruits of `KOTOBUKISHINSUI`.

FIG. 12 is a photograph of the side view of seeds of `KOTOBUKI SHINSUI`.

FIG. 13 is a photograph of leaf parts treated with AK toxin with a1000-fold dilution. wherein seven leaves each were taken from `KOTOBUKISHINSUI`, `Shinsui`, `Gold Nijisseiki` (U.S. Plant Pat. No. 8,529), and`Hosui` and placed in four columns. The four columns are, from left toright, `KOTOBUKI SHINSUI`, `Shinsui`, `Gold Nijisseiki`, and `Hosui`,respectively.

FIG. 14 is a photograph of petals of `Shinsui` (the top row), `KOTOBUKISHINSUI` (the second row), `Gold Nijisseiki` (the third row) and `Hosui`(the bottom row); wherein in each row the first, second, third andfourth petals were treated with crude toxin with 500-fold dilution,crude toxin with 1000-fold dilution, crude toxin with 10,000-folddilution and distilled water as a control, respectively.

FIG. 15 is a photograph of young fruits after 30 days from flowering(the lower row) and 45 days from flowering (the upper row) of `Shinsui`,`KOTOBUKI SHINSUI`, `Nijisseiki` (unpatented), `Gold Nijisseiki` and`Hosui`, from the left to the right, respectively, about 24 hours afterinoculation with spore of Alternaria alternata Japanese pear pathotypeisolate ML-10E.

FIG. 16 is a photograph of parts of the fourth leaves of, from the topto bottom rows, `Shinsui` `KOTOBUKI SHINSUI`, `Nijisseiki`, `GoldNijisseiki` and `Hosui` treated with AK toxin at a concentration of1×10⁻⁴, 5×10⁻⁵, 1×10⁻⁵, 5×10⁻⁶, 1×10⁻⁶, 1×10⁻⁷, 1×10⁻⁸ or 1×10⁻⁹ M (fromthe left to right columns). It is clear that `KOTOBUKI SHINSUI` is muchmore resistant to AK toxin than `Shinsui` because the concentrations ofAK toxin producing a similar blackening effect on the leaves differ byas much as two order of magnitude between `KOTOBUKI SHINSUI` and`Shinsui`.

FIG. 17 is a photograph of petals of, from the top to bottom rows,`Shinsui`, `KOTOBUKI SHINSUI`, `Nijisseiki`, `Gold Nijisseiki` and`Hosui` treated with AK toxin at a concentration of 1×10⁻⁴, 5×10⁻⁵,1×10⁻⁵, 5×10⁻⁶, 1×10⁻⁶, 1×10⁻⁷, 1×10⁻⁸ or 1×10⁻⁹ M (from the left toright columns). It is clear that `KOTOBUKI SHINSUI` is much moreresistant to AK toxin than `Shinsui` because the concentrations of AKtoxin producing a similar dark browning effect on the petals of`KOTOBUKI SHINSUI` and `Shinsui` differ by at least one to one and ahalf order of magnitude.

FIG. 18 illustrates the effects of AK toxin at different concentrationsranging from 5×10⁻⁵ M to 5 ×10⁻⁹ M or distilled water (from the left toright columns) on the first, second, third, fourth, fifth and sixthleaves of a current shoot of `KOTOBUKI SHINSUI` (shown in the top panel)or `Shinsui` (shown in the bottom panel). The degree of blackeningdepends on the concentration of the AK toxin and plant age in leafnumber. It is claer that AK toxin resistance is much higher in `KOTOBUKISHINSUI` than in `Shinsui` because the AK toxin concentrations producinga similar degree of blackening on the sixth leaves of `KOTOBUKI SHINSUI`and `Shinsui` differ by at least two and a half order of magnitude.

DESCRIPTION OF THE INVENTION

The characteristics of the new and distinct cultivar of Japanese peartree `KOTOBUKI SHINSUI` are as follows (In the following description,the color-coding is in accordance with The Royal Horticultural Society'sR.H.S. Colour Chart):

Tree:

Vigor.--Strong; new shoot growth averaged 180 cm in 1999.

Branch habit.--Medium.

Spurs.--Many; in 1999 an average of 14.7 per meter of a branch.

Number of axillary flower buds.--Few.

Time of bud break.--Medium, around April 15th at Tottori prefecture,Japan.

Production.--Medium productivity.

Cross-compatibility.--Cross compatible with `Chojuro` (unpatented) and`Nijisseki`, but incompatible with `Kosui` and `Shinsui`. The tree haslow self-compatibility and is manually pollinated.

Bark.--The bark of the new and old wood is hard. The size of thelenticels of the new and old wood are medium, and density thereof isalso medium (about 93 lenticels per 10 cm).

Trunk surface.--The color is R.H.S. Colour Chart Greyed-Orange 177A.

Branches (Shoot):

Length.--Medium.

Thickness.--Medium, about 9 mm.

Length of internode.--Short, about 3.7 cm.

Color.--R.H.S. Colour Chart Greyed-Brown 199B.

Density of pubescence.--Medium.

Angle between leaf bud and shoot.--Acute.

Leaves:

Shape.--Ovate.

Size.--Medium, (11 cm long by 7.1 cm wide).

Color (adult leaves).--R.H.S. Colour Chart 137A for adaxial leaves andR.H.S. Green 138D for abaxial leaves.

Length of petiole.--Short, about 2.2 cm.

Thickness of petiole.--Medium, about 2 mm.

Color of young leaves.--R.H.S. Red-Purple 60A.

Density of pubescence of young leaves.--Medium.

Flowers:

Flower number in a flower cluster.--Medium, about 8 flowers per cluster.

Size.--Medium, the average flower diameter is about 3.2 cm.

Color.--R.H.S. Red-Purple 57C corolla at early stages of blooming andfading to R.H.S. White 155D in later days, so that the color of theopened flower is white (R.H.S. White 155D).

Shape of petals.--Round.

Notch of petal margin.--Medium.

Number of petals.--Slightly more than medium, 5.0 per flower on average.

Color of anthers.--R.H.S. Red-Purple 60C.

Number of stamens.--Slightly more than medium, 21.4 on average.

Amount of pollen.--High.

Flowering time.--Middle of the season.

Flowering date and full bloom stage.--Around April 17th and April 20that the Tottori Prefecture, Japan. (Two days earlier than `Kosui` and twodays later than `Hosui`). The approximate duration of bloom of the newcultivar at Tottori Prefectural Experiment Station (Tottori-ken) wasfrom 7 to 9 days in 1992-1999.

Fruit:

Size.--294 g on average in 1992.

Shape.--Oblate.

Color of skin (unbagged fruit).--R.H.S. Small, Greyed-Orange 163A.

Calyx.--Almost all of the fruits are calyx deciduous, but some of thefruits are calyx perpetual.

Size of dots on fruit skin.--Medium.

Density of dots on fruit skin.--High.

Color of dots on fruit skin.--R.H.S. Gray-Yellow 162A.

Color of flesh.--R.H.S. Yellow-White 158C.

Flesh.--Between soft and medium and medium juicy. The firmness is about4.7 lbs. according to Magness-Teller's hardness meter index.

Length of peduncle.--Medium.

Thickness of peduncle.--Thin.

Color of peduncle.--R.H.S. Yellow-Green 152A.

Color of core.--R.H.S. Yellow-White 158D.

Shape of core.--Short conical.

Size of core.--Ratio of transverse diameter of core to transversediameter of fruit is medium, 25.4/84.6.

Seed cells.--Medium. 5.2 cells per fruit on average.

Size of seeds.--Medium, about 8 mm by 5 mm on average.

Color of seeds.--R.H.S. Black 202A.

Shape of seeds.--Oval.

Taste.--Highly sweet, the total sugar content of the fruit juice isabout 13.6%, medium in acidity, pH 4.7, and no astringency.

Bagging.--The bagged fruit has a slightly fine appearance than the fruitthat has not been bagged.

Maturity.--Ripening early in the season, e.g., August 15th-28th at theTottori Prefecture, Japan.

Productivity.--The production of a 6-year old immature tree of the newcultivar was 9.6 kg/tree and the productivity of a 26-year old adulttree of `Shinsui` was 126 kg/tree in 1998.

Use.--Suitable for dessert.

Keeping quality.--Can be kept for about 6 days at 20-25° C.

Resistance to Diseases:

The leaves, petals and young fruit (20, 30, 45 and 65 days afterblooming) were inoculated indoors with a 100 to 1000 fold dilution odAK-toxin (culture filtrate of Alternaria alternata Japanese pearpathotype) or with black spot disease spores (atomizing inoculation with5 ×10⁵ spores/ml of strain 15A or Alternaria alternata Japanese pearpathotype isolate ML-10E) for a disease resistance test (see FIGS.13-15).

Upon examination with black spot disease spore inoculation, the leavesof the original cultivar `Shinsui` were entirely blackened, whileblackening was found only on portions of the leaves of `KOTOBUKISHINSUI` (see Table 1). With AK toxin inoculation, treatment of theoriginal cultivar `Shinsui` with the toxin dilutions of 100 to 1000 foldresulted in rather extensive blackening on the affected parts of theleaves, but although `KOTOBUKI SHINSUI` showed similar results using 100to 500 fold dilutions, only slight blackening was found on the affectedparts of the leaves using a 1000 fold dilution (see Table 2). Toxintreatment of the petals gave results similar to those for the leaves. Inthe spore inocultion test on the young fruit, widespread symptoms werefound in the original cultivar `Shinsui`, while only small blackenedareas were found in `KOTOBUKI SHINSUI`.

Upon observation of the extent of onset of black spot disease in fieldcultivation, `KOTOBUKI SHINSUI` is clearly more resistant than theoriginal cultivar `Shinsui`, as `Shinsui` exhibited symptoms in theyoung shoots and fruit with considerable fruit abscission due to blackspot disease with non-bag cultivation, while `KOTOBUKI SHINSUI`exhibited only slight symptoms and no fruit abscission.

Thus, the disease resistance of `KOTOBUKI SHINSUI` is demonstrated to bestronger than that of `Shinsui`, although it is not a completeresistance, like `Kosui` or `Hosui`, but rather a medium level ofresistance similar to `Gold Nijisseiki`.

The disease control methods used for the resistant cultivars `Kosui` and`Hosui` can be adequately applied as the disease control methods for theinstant cultivar.

The present tree has no susceptibility to pear necrotic spot virus, andhas minor susceptibility to pear scab, pear canker and physalosporacanker.

Other cultural considerations:

Cold resistance.--Almost the same as that of other Japanese pears.

Core breakdown.--Absent.

Watercore.--Absent.

Fruit cracking.--Slightly apparent.

Culture.

Although the new cultivar has few axillary flower buds and many spurs,spurs have a tendency to form blind buds. However, this problem can besolved by adequate tree training and pruning methods.

The new cultivar of Japanese pear tree, `KOTOBUKI SHINSUI`, iscultivated and kept at the Institute of Radiation Breeding, NationalInstitute of Agrobiological Resources, MAFF and Tottori PrefecturalExperimental Station, Japan. `KOTOBUKI SHINSUI` bears fruits every year.

Since the new cultivar, `KOTOBUKI SHINSUI`, has a strong resistance toblack spot disease, and has excellent dessert quality, etc., the treesof the new cultivar can be conveniently and easily cultivated in variousagricultural districts.

                  TABLE 1                                                         ______________________________________                                        Reaction with inoculation of black spot disease                               spore to the fourth leaf of a current shoot                                   Variety line  Degree of blackening                                            ______________________________________                                        Kotobuki Shinsui                                                                            ±                                                            Shinsui       +                                                               Hosui         -                                                               Kosui         -                                                               Nijjiseiki    +                                                               Gold Nijjiseiki                                                                             ±                                                            ______________________________________                                         -: No reaction                                                                ±: Portions of leaves were blackened                                       +: Leaves were entirely blackened                                        

Table 1 shows the response of the fourth leaf of a current shoot of`KOTOBUKI SHINSUI`, `Shinsui`, `Hosui`, `Kosui`, `Nijisseiki` and `GoldNijisseiki` to an inoculation of black spot disease spore. According toTable 1, the inoculation produced only blackening in a portion of thefourth leaf of the current shoot of `KOTOBUKI SHINSUI`, but theinoculation made the fourth leaf of the current shoot of `Shinsui`entirely blackened.

                  TABLE 2                                                         ______________________________________                                        Assay with inoculation of toxin to a leaf of a current shoot                         Dilution                                                                      Ratio                                                                         ×100    ×500                                                        Position                                                             Variety  of leaf                                                              line     1      2      3    4    1    2    3    4                             ______________________________________                                        Kotobuki Shin-                                                                              ++                                                                              ++     ++   ++   ++   ++   ++   +                             sui                                                                           Shinsui         ++   ++                                                                              ++   ++   ++   ++   ++   ++                            Hosui           -      -                                                                             -    -    -    -    -    -                             Kosui           -      -                                                                             -    -    -    -    -    -                             Nijjiseiki                                                                                    ++++   ++   ++   ++   ++   ++   ++                            Gold            ++     +++  ++   ++   ++   ++   ++                            Nijjiseiki                                                                    ______________________________________                                               Dilution                                                                      Ratio                                                                                       Control                                                         ×1000   (Distilled water)                                                 Position                                                             Variety  of leaf                                                              line     1      2      3    4    1    2    3    4                             ______________________________________                                        Kotobuki Shin-                                                                             +  +      ± ± -    -    -    -                             sui                                                                           Shinsui         ++  ++ ++   ++   -    -    -    -                             Hosui           -     -                                                                              -    -    -    -    -    -                             Kosui           -     -                                                                              -    -    -    -    -    -                             Nijjiseiki                                                                                    +++    ++   ++   -    -    -    -                             Gold            +      +                                                                             ± ± -    -    -    -                             Nijjiseiki                                                                    ______________________________________                                         -: No reaction.                                                               ±: Slight blackening was observed at inoculation points.                   +: Blackened portion slightly larger than inoculation points was observed     ++: Considerably larger blackened portion than inoculation points was         observed.                                                                

Table 2 shows the response of a leaf of a new shoot of `KOTOBUKISHINSUI`, `Shinsui`, `Hosui`, `Kosui`, `Nijisseiki` and `GoldNijisseiki` to an inoculation of toxin. According to Table 2, theinoculation of the toxin with a 1/1000 dilution produced slightblackening at the inoculation points in the leaf of `KOTOBUKI SHINSUI`,while the inoculation of the toxin with the same degree of dilutionproduced a considerably larger blackened portion at the inoculationpoints in the leaf of `Shinsui`.

We claim:
 1. A new and distinct cultivar of Pyrus pyrifolia (Japanesepear) tree, substantially as herein illustrated and described,characterized by a significantly stronger resistance to black spotdisease